Gas pressurized hydraulic shock absorber assemblies are well known and have been used on vehicles for some time. Methods and apparatus for pressurizing such assemblies, and similar containers, are disclosed in issued U.S. patents.
U.S. Pat. Nos. 3,139,159, 4,114,866 and 4,131,139 each show the introduction of a pressurizing gas into a suspension unit by passing the gas past a displaceable end seal of the unit. Such a method is dependent upon the seal to move back into a sealing position to maintain the gas pressurized also, such units may be subject to depressurization during storage or use due to unintended displacement of the seal.
U.S. Pat. No. 3,975,259 shows a means of charging a shock absorber in which the piston rod, appropriately infigured, is positioned to enable introduction of a gas to the interior of a shock absorber. Recharging a shock using such an arrangement would appear to be difficult or impractical.
U.S. Pat. No. 3,081,587 discloses a method and apparatus for pressurizing an unsealed shock absorber assembly through a pre-formed opening and closing the opening using an inserted and welded plug.
U.S. Pat. No. 2,101,156 shows a machine for pressurizing a receptacle through a pre-formed opening and sealing the opening by placing a ball over it and then contacting the ball with an electrode to cause the ball to melt, flow into and sealingly unite with the opening.
Each of the disclosures in the two patents mentioned immediately above teach sealing a pre-formed opening in a liquid containing container. Pre-formed openings are disadvantageous as they must either be temporarily sealed or the container must be oriented and handled in a manner which does not allow the contained liquid to flow from the unit. Also, care must be taken to prevent the entry of contaminants, such as particulate matter or corrosive materials, into the container through the pre-formed opening prior to pressurization and sealing.
U.S. Pat. No. 3,736,645 shows a ball jammed into a pre-formed opening used to pressurize a shock absorber for a vehicle bumper. The ball is maintained in a sealing position in the opening by welding.